Characterizing Salinity and Salinity Matrixes in the Burdekin and Fitzroy Catchments, Queensland, Australia

抄録

In Australia, salinity is a significant issue plaguing freshwater systems, especially in catchments modified by mining activities. River salinity varies in composition from changes in aquifer lithology, natural salt deposits and salt accumulation due to land altering activities (e.g., mining and agriculture). Complex salinity matrixes arise when different salinity sources and compositions are diluted into freshwater systems. Monitoring waterway salinity and characterizing salinity matrixes is vital to mitigating adverse impacts on agriculture, drinking water supplies and ecosystem health. However, to date, few studies have focused on characterizing salinity in freshwater systems based on source. In this paper, case studies drawn from the Burdekin and Fitzroy catchments, Queensland, are characterized for different salinities associated with mining and natural geogenic mineralization. Salinity coefficients (ke), a ratio of total dissolved solids (TDS in mg/L) to electrical conductivity (EC in µS /cm), are utilized to identify variations in salinity composition. Long-term water quality data (1964-2023) is retrieved from the Queensland Government’s water monitoring program. Findings indicate that mining activities in both catchments have a significant influence on freshwater salinity matrixes, driving lower k_e values (0.561-0.587). A novel method for analyzing long-term k_e data is introduced, utilizing the slope (m) of k_e in cumulative distribution plots. Significant variations in slope in the Fitzroy (m: 9.6, 5.3, 2.3) and in the Burdekin River (m: 8.9, 1.6, 1.0, 0.7) reveal influences on local mineralization and industry, not readily evident when only considering average k_e. This study demonstrates that utilizing known geochemical, EC and TDS relationships and k_e is an effective preliminary method for identifying salinity complexity, composition and source. Salinity in the Fitzroy catchment surpasses aquatic toxicity thresholds (EC50: 2410 µS/cm), revealing significant risks to freshwater aquatic species.